The present invention relates generally to helical scan video tape recorders, and in particular to a circuit arrangement for recording an index signal at the beginning of a video program which enables a program search circuit to quickly detect the beginning of a desired program.
It is known in the art to record an index signal at the beginning of each video program to allow it to be quickly searched during playback. The index signal currently in use is a train of rectangular pulses at a repetition frequency of 30 Hz which is coupled through a switched connection to a full erase head of the video recorder while decoupling a high frequency signal. The high frequency signal is then applied to the erase head after the index signal has been recorded in order to erase a prerecorded material. Since the full erase head is located upstream of the video head in the direction of motion of video tape, the beginning of the video program overlaps with the portion in which the index signal is recorded. Due to the relatively low frequency of the index signal in relation to the speed of tape, the index signal is recorded in a deeper area of the tape and the video signal is recorded in the tape's upper area. However, since the index signal is directly recorded in the video tape without high frequency bias and since the video signal has been converted to a low frequency range of the video spectrum prior to recording, the index signal interferes with the video signal detected from the overlapped portion of the tape during playback modes.